Brother MFC-8220 Service Manual page 161

CHAPTER 5 PERIODIC MAINTENANCE
In order to deal with this unexpected usage and maintain the steady print density, the machine
can be initialized the developing bias compulsorily in the following procedure.
<Initialization Procedure>
(1) Open the front cover.
(2) Press the buttons in the following order. "Clear/Back", "*", "0 (zero)", "0 (zero)"
(3) Close the front cover.
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